How can a derived C++ class clone itself via a base pointer?

Question

Here\'s what I\'m trying to do (this code doesn\'t work):

class Base
{
    virtual Base *clone() { return new Base(this); }
    virtual void ID() { printf(\"         


        

Answer 1

That code is riddled with syntactical errors. Perhaps most significantly, Derived doesn't inherit from Base. Secondly, aside from the syntactical errors (probably simple typos), Base obviously needs a virtual destructor. The clone method pretty much demands that you can call operator delete on a base pointer (Base*).

class Base
{
public:
    virtual ~Base() {}
    virtual Base* clone() const { return new Base(*this); }
    virtual void ID() const { printf("BASE"); }
};

class Derived: public Base
{
public:
    // [Edit] Changed return type to Derived* instead of Base*.
    // Thanks to Matthieu for pointing this out. @see comments below.
    virtual Derived* clone() const { return new Derived(*this); }
    virtual void ID() const { printf("DERIVED"); }
};

int main()
{
    Derived d;
    Base* bp = &d;

    Base* bp2 = bp->clone();
    bp2->ID(); // outputs DERIVED as expected
    delete bp2;
}